Osmotic systems for delivering a beneficial agent to an environment of use are known to the art in U.S. Pat. Nos. 3,854,770 and 3,916,899. The osmotic systems disclosed in these patents are made with a semipermeable wall that surrounds a compartment containing agent. The semipermeable wall is permeable to an external fluid and substantially impermeable to agent. The system has a passageway through the semipermeable wall for delivering agent from the compartment to the environment of use. These systems are extraordinarily effective for delivering an agent that is soluble in fluid that enters the compartment and exhibit an osmotic pressure gradient across the semipermeable wall against the fluid, and also for delivering an agent that has limited solubility in the fluid. In this latter embodiment, the agent is mixed with an osmotically effective compound that is soluble in the fluid and exhibits an osmotic pressure gradient across the semipermeable wall against the fluid.
These prior art osmotic systems release their agent by imbibing fluid through the semipermeable wall into the compartment at a rate determined by the permeability of the semipermeable wall and the osmotic pressure gradient across the semipermeable wall producing a solution of soluble agent, or a solution of soluble compound containing agent, which solution in either operations is dispensed at a controlled rate through the passageway to the exterior of the device over a prolonged period of time.
The prior art described above represents an outstanding and pioneering advancement in the delivery art. The osmotic systems are useful for dispensing beneficial agents to the environment of use. Now, it has been found, these osmotic systems can have novel, inventive improvements that enhance the usefulness of the systems and broaden their application. For example, osmotic systems made according to the invention have an agent distribution zone and a second wall. These act together as a single entity, and they dispense an agent released from the system over a broader receptive area per unit of time. That is, they produce an agent distribution profile in both time and space. It will be appreciated by those versed in the art, these improvements represent a substantial contribution to the delivery art. For example, the present systems can dispense an agent over a wider area than is possible with a single passageway system, and they can decrease the amount of agent presented to a receptor site. Accordingly, the systems of this invention can be advantageously used for lessening the possible incidence of unwanted agent-receptor interreaction. It will, therefore, be appreciated the osmotic systems of this invention have a positive value in the medical and veterinary arts. In addition, the properties of the second wall can be selected such that the rigidity of the system can be programmed.